Optical device for microscopic observation

ABSTRACT

An optical device for microscopic observation  4  comprises: a cold stop  13  having openings  13   d,    13   e  corresponding to a low-magnification microscope optical system  5  and being a stop member arranged in a vacuum vessel  12  to let the light from the sample S pass to the camera  3 ; a warm stop  10  having an opening  14  corresponding to a high-magnification microscope optical system  5  and being a stop member arranged outside the vacuum vessel  12  to let the light from the sample S pass toward the cold stop  13 ; and a support member  11  supporting the warm stop  10  so that the warm stop can be inserted to or removed from on the optical axis of the light from the sample S, wherein the warm stop  10  has a reflective surface  15  on the camera  3  side and wherein the opening  14  is smaller than the openings  13   d,    13   e.

TECHNICAL FIELD

The present invention relates to an optical device for microscopicobservation provided for enlarged observation of light from an object.

BACKGROUND ART

Optical devices for observing light of specific wavelength such asinfrared light from an object have been used heretofore. Such opticaldevices are provided with a mechanism for suppressing influence of lightfrom the part other than the object. For example, Patent Literature 1below discloses an infrared detecting device having a toroidalwarmshield comprising segments. This infrared detecting device isprovided with a vacuum window in a front face of a coldshieldsurrounding an infrared detector, and three toroidal reflective membersare arranged in front of this vacuum window. These toroidal reflectivemembers have respective openings in their centers and these openings arearranged as aligned on a central axis so that they are located insymmetry with respect to the central axis of the detecting device. Thesizes of the respective openings are set according to the diameter of anoptical image to be detected by the infrared detector. Inside surfacesof these toroidal reflective members are toroidal surfaces.

Patent Literature 2 below discloses an infrared optical device forletting infrared light from an object pass through an interchangeablelens and impinge on a detector element, this infrared optical device isequipped with a Dewar vessel provided around the detector element andtwo mirror apertures provided outside the Dewar vessel, and these mirrorapertures are arranged as movable along the optical axis of theinterchangeable lens. Mirror surfaces are provided on the inside of themirror apertures, the infrared light from the object travels throughopening portions of the mirror apertures to reach the detector elementin the Dewar vessel, and infrared light emanating from the part otherthan the object is prevented from impinging on the detector element,because only the cooled part or only the detector element is seen whenthe mirror surfaces are viewed from the detector element. As a result,good imaging performance can be achieved.

CITATION LIST Patent Literature

Patent Literature 1: U.S. Pat. No. 4,820,923

Patent Literature 2: Japanese Patent Application Laid-Open

Publication No. H06-160696

SUMMARY OF INVENTION Technical Problems

In the infrared detecting device described in the foregoing PatentLiterature 1, however, since the sizes of the openings of the toroidalreflective members are set according to the aperture of the coldshield,it is difficult, with a changeover of the magnification of the opticalsystem located on the object side, to make an image according to thechanged magnification impinge on the detector element.

The infrared optical device described in the foregoing Patent Literature2 allows suitable observation of the object with use of interchangeablelenses of various numerical apertures at different magnifications bymoving the mirror apertures along the optical axis of theinterchangeable lens upon a change of the object-side interchangeablelens, but it requires a mechanism for adjusting the positions of themirror apertures, which tends to increase the scale of the device. Ifthere is a large difference between image-side numerical apertures ofinterchangeable lenses as interchanged objects, it is necessary toensure a large adjustable distance for the mirror apertures, which tendsto increase the scale of the device.

The present invention has been accomplished in view of the foregoingproblems and it is an object of the present invention to provide anoptical device for microscopic observation enabling a changeover betweena plurality of observation magnifications of the object and allowingeasy implementation of downsizing of the device.

Solution to Problems

In order to solve the above problems, an optical device for microscopicobservation according to an aspect of the present invention is anoptical device for microscopic observation which makes light from anobject incident on an imaging element, the optical device comprising: acold stop which has a first opening corresponding to an optical systemon the object side having a first magnification and which is arranged ina vacuum vessel to let the light from the object pass to the imagingelement; a warm stop which has a second opening corresponding to anoptical system on the object side having a second magnification andwhich is a stop member arranged outside the vacuum vessel to let thelight from the object pass toward the cold stop; and a support memberwhich supports the warm stop so that the warm stop can be inserted to orremoved from on the optical axis of the light from the object, whereinthe warm stop has a reflective surface on the imaging element side andwherein the second opening is smaller than the first opening.

In this optical device for microscopic observation, when the opticalsystem set at the first magnification is used as the object-side opticalsystem, the warm stop is set off from on the optical axis, whereby thelight from the object impinges on the imaging element while beingnarrowed down by the cold stop with the first opening corresponding toan NA of the optical system, which reduces background noise in adetected image by the imaging element. Furthermore, when the opticalsystem set at the second magnification is used as the object-sideoptical system, the warm stop with the second opening corresponding toan NA of the optical system is arranged on the optical axis, whereby thelight from the object is narrowed down according to a beam thereof andthereafter passes through the cold stop to impinge on the imagingelement. Here, since the second opening is smaller than the firstopening, the background noise can be reduced corresponding to opticalsystems with multiple magnifications even if the support member forinserting and removing the warm stop is located outside the vacuumvessel, which can simplify the structure of the support member. Sincethis support member is disposed in directions intersecting with theoptical axis of the optical system, downsizing of the support member isalso readily realized. As a result, it becomes feasible to implement achangeover between a plurality of observation magnifications, whilereducing the background noise for optical systems with multipleobservation magnifications, and to readily realize downsizing of thedevice.

Advantageous Effect of Invention

The present invention enables reduction in background noise for opticalsystems with multiple observation magnifications and easy implementationof downsizing of the device.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic configuration diagram of a microscope deviceaccording to a preferred embodiment of the present invention.

FIG. 2 is a perspective view showing an optical device for microscopicobservation 4 shown in FIG. 1, which is cut along a central axis.

FIG. 3 is a perspective view showing the optical device for microscopicobservation 4 shown in FIG. 1, which is cut along the central axis.

FIG. 4 is a plan view showing a state of incidence of a beam from asample S in the optical device for microscopic observation 4 wherein awarm stop 10 is removed as shown in FIG. 2.

FIG. 5 is a plan view showing a state of incidence of a beam from thesample S in the optical device for microscopic observation 4 wherein thewarm stop 10 is inserted as shown in FIG. 3.

FIG. 6 is a plan view of the warm stop 10 in FIGS. 2 and 3.

FIG. 7 is a plan view showing an observation range of an imaging element16 with respect to a reflective face 15 b of the warm stop 10 in FIG. 6.

FIG. 8 is a plan view showing an observation range of the imagingelement 16 set by the optical device for microscopic observation 4 inFIG. 3.

FIG. 9 is a plan view showing the major part of an optical device formicroscopic observation 24 according to the second embodiment of thepresent invention.

FIG. 10 is a plan view showing the major part of an optical device formicroscopic observation 44 according to the third embodiment of thepresent invention.

FIG. 11 is a plan view showing the major part of an optical device formicroscopic observation 64 according to the fourth embodiment of thepresent invention.

FIG. 12 is a plan view of a warm stop 110 being a modification exampleof the present invention.

FIG. 13 is a plan view of a warm stop 210 being another modificationexample of the present invention.

FIG. 14 is a plan view of a warm stop 310 being another modificationexample of the present invention.

FIG. 15 is a plan view of a warm stop 90 being another modificationexample of the present invention.

DESCRIPTION OF EMBODIMENTS

Preferred embodiments of optical devices for microscopic observationaccording to the present invention will be described below in detailwith reference to the drawings. Identical or equivalent portions will bedenoted by the same reference signs in the description of the drawings,without redundant description.

First Embodiment

FIG. 1 is a schematic configuration diagram of a microscope device 1 forluminescence observation according to the first embodiment of thepresent invention. The microscope device 1 shown in the same drawing iscomposed of a dark box 2, a camera (imaging element) 3 that can detectinfrared light emitted from a sample (object) S set in the dark box 2,an optical device for microscopic observation 4 attached to the camera3, and a microscope optical system 5 arranged between the camera 3integrated with the optical device for microscopic observation 4, andthe sample S. This microscope optical system 5 is an optical system forforming an infrared image of the sample S at a desired magnification inthe camera 3, and is configured in a structure wherein a macro opticalsystem 7 incorporating a lens with a relatively low magnification and amicro optical system 8 incorporating a lens with a higher magnificationthan the magnification of the macro optical system 7 are supported sothat they can be changed over from one to the other by an optical systemchangeover mechanism 6. This microscope optical system 5 implements sucha changeover as to locate either of the macro optical system 7 and themicro optical system 8 between the sample S and the optical device formicroscopic observation 4, whereby infrared light emitted from thesample S is incident into the camera 3 through the objective opticalsystem according to the desired magnification.

The optical device for microscopic observation 4 is an optical devicefor combining the camera 3 capable of detecting the infrared light, withthe microscope optical system 5 for forming the infrared image of thesample S in the camera 3, while allowing a changeover between themagnifications. FIGS. 2 and 3 are perspective views showing the opticaldevice for microscopic observation 4 cut along the central axis. FIG. 2shows a use state of the optical device for microscopic observation 4with the microscope optical system 5 being changed over to the macrooptical system 7, and FIG. 3 a use state of the optical device formicroscopic observation 4 with the microscope optical system 5 beingchanged over to the micro optical system 8.

The optical device for microscopic observation 4 is provided with arelay lens 9 for re-imaging an image plane where the beam of infraredlight from the macro optical system 7 and the micro optical system 8 isfocused, a warm stop 10 being a stop member with a light shield propertyfor narrowing down the beam incident from the relay lens 9 side, asupport member 11 supporting this warm stop 10 so that it can beinserted to or removed from on the optical axis of the relay lens 9, avacuum vessel 12 of a nearly cylindrical shape, and a cold stop 13arranged on the optical axis of the relay lens 9 in the vacuum vessel 12and being a stop member with a light shield property for narrowing downthe beam incident from the relay lens 9 side.

The warm stop 10 has an approximate disk shape, an opening 14 of anearly circular shape is formed in a center thereof, and a reflectivesurface 15 is formed on the opposite side to the relay lens 9 locatedoutside the opening 14. This warm stop 10 is fixed to the support member11 of an elongated shape and is supported so as to be slidable indirections perpendicular to the optical axis of the relay lens 9 by thesupport member 11. Namely, the warm stop 10 is arranged in such a mannerthat it can be inserted or removed between a position where it isremoved from an exit face 9 a of the relay lens 9 (FIG. 2) and aposition where it is inserted so as to face the exit face 9 a of therelay lens 9 (FIG. 3). When the warm stop 10 is inserted, the warm stop10 is located at the position corresponding to the pupil position of themicro optical system 8 in the microscope optical system 5 in a state inwhich the center of the opening 14 thereof is coincident with theoptical axis of the relay lens 9. This position corresponding to thepupil position of the micro optical system 8 is preferably near thepupil position and if the pupil position is present in the vacuum vessel12, it is a position as close to the pupil position as possible and,specifically, a position proximate to a window 12 a on the sample S sideof the vacuum vessel 12.

The cold stop 13 is arranged inside the vacuum vessel 12 maintained in alow temperature state by an unillustrated cooling device and isconfigured so that double stop members 13 b, 13 c are integrally formedinside a tubular member 13 a of a cylindrical shape. These stop members13 b, 13 c have an approximate disk shape and openings 13 d, 13 e of anearly circular shape are formed in their centers so that the centers ofthe openings 13 d, 13 e are coincident with the optical axis of therelay lens 9. The window 12 a of a circular shape is provided in an endface on the relay lens 9 side of the vacuum vessel 12 and the beam fromthe sample S having passed through the relay lens 9 travels through thewindow 12 a to enter the cold stop 13 in the vacuum vessel 12.Furthermore, the tip section of the camera 3 is hermetically connectedto an opening part 12 b of a circular shape on the opposite side to therelay lens 9 in the vacuum vessel 12, whereby an image detection planeof an imaging element built in the camera 3 is arranged so as to facethe window 12 a with the cold stop 13 in between. This configurationallows the entire cold stop 13 and the tip section of the camera 3 to bemaintained in a low temperature state.

Next, the relationship between the sizes of the warm stop 10 and thecold stop 13 will be described. FIG. 4 is a plan view showing a state ofincidence of the beam from the sample S in the optical device formicroscopic observation 4 wherein the warm stop 10 is removed, and FIG.5 a plan view showing a state of incidence of the beam from the sample Sin the optical device for microscopic observation 4 wherein the warmstop 10 is inserted.

With reference to FIG. 4, when the microscope optical system 5 ischanged over to the macro optical system 7, it is necessary to use alens with a large NA for obtaining high sensitivity even with the use ofthe macro optical system 7 having the relatively low magnification andtherefore the exit pupil diameter of the macro optical system 7 becomeslarger in accordance therewith. In this case, the beam B₁ having beenemitted from the sample S and having passed through the macro opticalsystem 7 is re-focused by the relay lens 9 to travel through theopenings 13 d, 13 e of the stop members 13 b, 13 c of the cold stop 13to impinge on the imaging element 16 built in the camera 3. In order toprevent the imaging element 16 from observing radiation from thesurroundings on this occasion, the inner diameters of the openings 13 d,13 e are set to sizes matching the magnification of the macro opticalsystem 7 so as to match the diameter of the beam B₁. The “sizes matchingthe magnification” stated herein refer to sizes ranging from 100% to120% of the diameter of the beam B₁ including an error in a permissiblerange according to the diameter of the beam B₁ determined by themagnification of the macro optical system 7, and do not have to belimited to sizes perfectly coincident with the diameter of the beam B₁.

With reference to FIG. 5, when the microscope optical system 5 ischanged over to the micro optical system 8, the NA needed in the microoptical system 8 with the relatively high magnification is smaller thanthat in the macro optical system 7 and therefore the exit pupil diameterof the micro optical system 8 becomes smaller according thereto.Specifically, the NA of the micro optical system 8 is that of the macrooptical system 7 divided by several tens. In this case, the beam B₂having been emitted from the sample S and having passed through themicro optical system 8 is re-focused by the relay lens 9 to successivelytravel through the opening 14 of the warm stop 10 and the openings 13 d,13 e of the stop members 13 b, 13 c of the cold stop 13 to impinge onthe imaging element 16 built in the camera 3. In order to prevent theimaging element 16 from observing radiation from the surroundings onthis occasion, the inner diameter of the opening 14 is set to a sizematching the magnification of the micro optical system 8 so as to matchthe diameter of the beam B₂. This results in setting the inner diameterof the opening 14 smaller than the inner diameters of the openings 13 d,13 e. The “size matching the magnification” stated herein refers to asize ranging from 100% to 120% of the diameter of the beam B₂ includingan error in a permissible range according to the diameter of the beam B₂determined by the magnification of the micro optical system 8, and doesnot have to be limited to a size perfectly coincident with the diameterof the beam B₂.

Next, the configuration of the warm stop 10 will be described in detail.FIG. 6 shows a plan view of the warm stop 10.

A reflective surface 15 coated with a high-reflectance material such asgold or silver is formed as a surface on the imaging element 16 side ofthe warm stop 10. This reflective surface 15 is produced so that areflective face 15 a with a gentle slope relative to a face including anopening edge of the opening 14 and a reflective face 15 b with a steepslope relative to the face including the opening edge of the opening 14are continuously formed in this order from the opening edge of theopening 14 toward the outside. Specifically, the reflective face 15 a isa plane approximately parallel to the face including the opening edge ofthe opening 14 and the reflective face 15 b a concave face (e.g., aspherical face or the like) whose inclination gradually increases towardthe outside. The reflective face 15 b may have a conical surface shapewhose inclination is constant. The shapes of these reflective faces 15a, 15 b are set so as to project an image of the cold stop 13 onto theimaging element 16 and so as not to project an image of the imagingelement 16 itself thereto.

Specifically, when the reflective face 15 b of the warm stop 10 adoptedis a spherical surface shape with the center of a sphere on the opticalaxis, the radius of curvature R of the reflective face 15 b is setdifferent from a distance between the imaging element 16 and the warmstop 10 so that normals to the reflective face 15 b are not directeddirectly to the imaging element 16, in order to prevent luminescence andreflected and scattered light from the imaging element 16 from beingagain focused on the imaging element 16. Specifically, the radius ofcurvature R is set to be sufficiently larger than the same distancebetween the imaging element 16 and the warm stop 10. When a conicalsurface is adopted as the reflective face 15 b of the warm stop 10,intersecting positions of normals to the reflective face 15 with theoptical axis are set sufficiently apart from the imaging element so thatthe normals are not directed directly to the imaging element 16, inorder to prevent luminescence and reflected and scattered light from theimaging element 16 from being again focused on the imaging element 16.

As shown in FIG. 7, the reflective face 15 b of the warm stop 10 isformed so that the radius of curvature at a slope of portionscorresponding to the diameter of the opening 13 d of the stop member 13b of the cold stop 13 or portions intersecting with chain lines in thesame drawing is set to not more than about twice the distance betweenthe imaging element 16 and the warm stop 10. This is a condition thatlines of sight extending from the imaging element 16 are returned to theinterior of the cold stop 13 whereby external radiation is not guided tothe imaging element 16. In more detail, when L is the distance betweenthe imaging element 16 and the warm stop 10, N_(m) NA of the reflectiveface 15 b, N_(e)=N_(m)L/R (R is the radius of curvature of thereflective face 15 b) an effective inclination in NA equivalent at theedge position of the reflective face 15 b, N_(c) an angle to theperiphery of the cold stop 13 in NA equivalent when viewed from the edgeposition of the reflective face 15 b, and N_(d) an NA of the imagingelement 16 when viewed from the reflective face 15 b, the condition thatthe outside of the cold stop 13 is never continually seen from theimaging element 16 is given by Expression (1) below;

N _(c) >N _(m) +N _(d)−2N _(e)  (1).

Therefore, based on the above Expression (1), the radius of curvature Rof the reflective face 15 b is set so as to satisfy Expression (2)below;

R<2N _(m) L/(N _(m) +N _(d) −N _(c))  (2).

A angle in NA equivalent is the result of conversion of the angle by asin function.

Furthermore, the inclination of the portions corresponding to thediameter of the opening 13 d of the stop member 13 b of the cold stop 13in the reflective face 15 b of the warm stop 10 is set to not more than45°. This is a condition necessary for preventing radiation from aclearance between the warm stop 10 and the cold stop 13 from impingingon the imaging element 16. When the inclination is set small in thismanner, the thickness of the warm stop 10 can be made smaller and anappropriate optical system can be readily formed by the warm stop 10.

An observation range of the imaging element 16 set with the warm stop 10being inserted, in the optical device for microscopic observation 4 ofthe foregoing configuration will be described with reference to FIG. 8.

As shown in the same drawing, the inside reflective face 15 a of thewarm stop 10 deflects lines of sight S₁, S₂ extending from the imagingelement 16, to a cooled portion of either stop member 13 b or 13 c ofthe cold stop 13. In conjunction therewith, scattered light andreflected light generated by scattering and reflection of the beam B₂ byan imaging area of the imaging element 16 is reflected to the outside ofthe imaging element 16 by the reflective face 15 a and is thus preventedfrom impinging on the imaging element 16. By the outside reflective face15 b of the warm stop 10, a line of sight S₃ extending from the imagingelement 16 is deflected to a cooled portion of the stop member 13 b ofthe cold stop 13 and thus is prevented from being directed toward a warmpart outside the stop member 13 b. In conjunction therewith, scatteredlight and reflected light generated on the imaging area of the imagingelement 16 is reflected to the outside of the imaging element 16 by thereflective face 15 b and thus is prevented from impinging on the imagingelement 16.

In the optical device for microscopic observation 4 described above,when the macro optical system 7 set at the low magnification is used asthe microscope optical system 5 on the sample S side, the warm stop 10is removed from on the optical axis, whereby the light from the sample Sis narrowed down by the cold stop 13 having the openings 13 d, 13 ematching the NA of the macro optical system 7, to impinge on the imagingelement 16, which reduces the background noise in the detected image bythe imaging element 16. Furthermore, when the micro optical system 8 setat the high magnification is used as the microscope optical system 5 onthe sample S side, the warm stop 10 with the opening 14 matching the NAof the micro optical system 8 is set on the optical axis, whereby thelight from the sample S is narrowed down according to the beam thereofand then passes through the cold stop 13 to impinge on the imagingelement 16. Since the opening 14 of the warm stop 10 is smaller than theopenings 13 d, 13 e of the cold stop 13 herein, the infrared image canbe suitably narrowed down corresponding to the microscope optical system5 with multiple magnifications even if the support member 11 forinsertion/removal of the warm stop 10 is located outside the vacuumvessel 12; therefore, the structure of the support member 11 issimplified. Since this support member 11 is provided in the directionsintersecting with the optical axis of the microscope optical system 5,downsizing of the support member 11 is also readily implemented. As aresult, it is feasible to reduce the background noise with a changeoverbetween observation magnifications of the sample S and to readilyrealize downsizing of the optical device for microscopic observation 4.

Since the support member 11 is configured so that the opening 14 of thewarm stop 10 can be inserted or removed at the position proximate to thewindow 12 a on the sample S side of the vacuum vessel 12, i.e., at theposition corresponding to the pupil position of the micro optical system8, when the high-magnification micro optical system 8 is used, theinfrared image of the sample S can be narrowed down in accordance withthe diameter thereof.

In the optical device for microscopic observation 4, the reflectivesurface 15 provided in the warm stop 10 causes the imaging element 16 toobserve the light from the cold stop 13 but not to observe the lightreflected by the imaging element 16. This allows both of spot noise andbackground noise to be reduced in the detected image by the imagingelement 16, in use of the microscope optical system 5 on the sample Sside while being changed over.

In the conventional microscope apparatus, for using both of ahigh-magnification objective lens and a low-magnification objectivelens, it is first necessary to make the camera-side NA sufficientlylarge, for effective use of the low-magnification lens. Specifically,when the magnification of the low-magnification lens for the camera isrepresented by a and the NA thereof is n, the camera-side NA needs to beset to n/a. However, since the NA necessary for the high-magnificationlens is that for the low-magnification lens divided by several tens, thecold stop for adjustment of the camera NA needed to suit the NA of thelow-magnification lens, for effective use of the two lenses. For thisreason, the conventional microscope apparatus observed the radiationfrom the surroundings through the excess NA portion in use of thehigh-magnification lens, so as to result in increase of backgroundnoise. In order to solve the problem of background noise, it iseffective to change the size of the cold stop according to the objectivelens. However, since the cold stop is usually arranged in vacuum andcooled at ultralow temperature, it is difficult to provide a mechanismfor change of size. In contrast to it, the present embodiment involvesthe insertion/removal of the warm stop 10 outside the vacuum vessel 12in accordance with the magnification of the microscope optical system 5on the sample S side, thereby achieving the same effect as decrease ofthe size of the cold stop. Since the position of the warm stop 10 is notlimited by the position of the exit pupil, there is no need for designof dedicated objective lenses, which facilitates optical design of theentire device.

The infrared optical device described in the prior Literature (JapanesePatent Application Laid-Open Publication No. H06-160696) allows suitableobservation with interchangeable lenses of various image-side numericalapertures by moving the mirror apertures along the optical axis of theinterchangeable lens upon a changeover of the object-sideinterchangeable lens, but it requires the mechanism for fine adjustmentof the positions of the mirror apertures, which tends to increase thescale of the device. If there is a large difference between thenumerical apertures of interchangeable lenses as interchanged objects,it is necessary to ensure a large adjustable distance for the mirrorapertures, which tends to increase the scale of the device. In contrastto it, since the optical device for microscopic observation 4 of thepresent embodiment is provided with the support member 11 forinsertion/removal of the warm stop 10 in the directions intersectingwith the optical axis of the microscope optical system 5, there is noneed for the mechanism for fine adjustment nor for ensuring the distancein the optic-axis direction, which facilitates downsizing of the device.

Since the reflective face 15 a and the reflective face 15 b arecontinuously formed from the opening 14 side toward the outside in thereflective surface 15 of the warm stop 10, it is feasible to set thedevice so as to prevent the imaging element 16 from observing radiantheat from the part other than the cold stop 13 and to make the reflectedlight by the imaging element 16 itself unlikely to be observed.

Since the radius of curvature of the reflective face 15 b of the warmstop 10 is set to not more than twice the distance between the imagingelement 16 and the warm stop 10, it is feasible to make radiation fromthe high-temperature part outside the cold stop 13 unlikely to impingeon the imaging element 16.

Furthermore, since the opening 14 of the warm stop 10 is smaller thanthe openings 13 d, 13 e of the cold stop 13, even if the microscopeoptical system 5 on the sample S side is used as changed over, thebackground noise in the detected image can be reduced corresponding tothe NA of the microscope optical system 5.

Second Embodiment

FIG. 9 is a plan view showing the major part of an optical device formicroscopic observation 24 according to the second embodiment of thepresent invention. The optical device for microscopic observation 24 ofthe present embodiment is different in the shape of the reflectivesurface 15 of the warm stop 10 from the optical device for microscopicobservation 4 according to the first embodiment.

Specifically, the warm stop 10 of the optical device for microscopicobservation 24 has a reflective face 15 c of a planar shape formed alongthe face including the opening edge of the opening 14, from the openingedge of the opening 15 toward the outside. The reflective face 15 c ofthis shape deflects a line of sight S₄ extending from the imagingelement 16, to a cooled part of either stop member 13 b or 13 c of thecold stop 13. In conjunction therewith, scattered light and reflectedlight generated by scattering and reflection of the beam B₂ on theimaging area of the imaging element 16 is reflected by the reflectiveface 15 c to the outside of the imaging element 16, so as not to impingeon the imaging element 16.

Third Embodiment

FIG. 10 is a plan view showing the major part of an optical device formicroscopic observation 44 according to the third embodiment of thepresent invention. The optical device for microscopic observation 44 ofthe present embodiment is different from the optical device formicroscopic observation 4 according to the first embodiment, in theshape of the reflective surface 15 of the warm stop 10 and in that thewarm stop 10 and the support member 11 supporting it are separated fromthe vacuum vessel 12 housing the cold stop 13.

Namely, the warm stop 10 is supported by the support member 11 so thatit can be inserted to or removed from on the optical axis of the relaylens 9 at a position apart from the window 12 a of the vacuum vessel 12.An optical system such as a mirror may be placed between the warm stop10 and the window 12 a and this optical system may be arranged to changethe direction of the beam B2 passing through the warm stop 10, while theimaging element 16 and the cold stop 13 are arranged off the opticalaxis of the relay lens 9. This can avoid increase in the scale of theoptical device for microscopic observation 44.

The warm stop 10 of the optical device for microscopic observation 24has a reflective face 15 d of a concave shape whose inclination relativeto the face including the opening edge of the opening 14, graduallyincreases from the opening edge of the opening 14 to the outside. Byadopting the reflective face 15 d of the concave shape, it becomesfeasible to readily set the shape to reflect the light from the coldstop 13 to the imaging element 16. The reflective face 15 d of thisshape deflects lines of sight S₅, S₆, and S₇ extending from the imagingelement 16, toward the cooled part inside the cold stop 13. Inconjunction therewith, scattered light and reflected light generated byscattering and reflection of the beam B₂ is reflected to the outside ofthe imaging element 16 by the reflective face 15 d, so as not to impingeon the imaging element 16.

Fourth Embodiment

FIG. 11 is a plan view showing the major part of an optical device formicroscopic observation 64 according to the fourth embodiment of thepresent invention. The optical device for microscopic observation 64 ofthe present embodiment is different from the optical device formicroscopic observation 44 according to the third embodiment, in that anauxiliary warm stop 70 is provided near the outside of the window 12 aof the vacuum vessel 12 between the warm stop 10 and the cold stop 13.

This auxiliary warm stop 70 is a light shield member having anapproximate disk-like shape and is arranged along the window 12 a of thevacuum vessel 12 so that its central axis coincides with the opticalaxis of the relay lens 9. A circular opening 74 having a diametersufficiently larger than the diameter of the beam B2 and facing theopening of the cold stop 13 is formed in a central region of theauxiliary warm stop 70. Furthermore, a reflective face 75 of a planarshape is formed as an outside face of the opening 74 on the window 12 aside of the auxiliary warm stop 70.

As equipped with such auxiliary warm stop 70, a line of sight S₈extending from the imaging element 16 to the outside of the warm stop 10is deflected to the cooled part of the cold stop 13 by the reflectiveface 75 of the auxiliary warm stop 70. In conjunction therewith,scattered light and reflected light directed from the imaging area ofthe imaging element 16 to the outside of the warm stop 10 is reflectedto the outside of the cold stop 13 by the reflective face 75, so as notto impinge on the imaging element 16.

The optical device for microscopic observation 64 of this configurationcan prevent the reflected light and scattered light from the imagingelement 16 from again impinging on the imaging element 16 and can makethe light from the high-temperature part unlikely to impinge on theimaging element 16 even with decrease in the diameter of the warm stop10. As a result, the device can be downsized and optical design becomeseasier.

The present invention is by no means intended to be limited to theforegoing embodiments. For example, the number of warm stops is notlimited to a specific number, but may be increased or decreasedaccording to the number of objective lenses used as changed over fromone to another on the sample S side. The reflective face 75 formed onthe face outside the opening 74 on the window 12 a side of the auxiliarywarm stop 70 does not have to be limited to the planar shape, but it maybe a concave shape such as a spherical surface, or a conical surfaceshape.

The shape of the reflective face of the warm stop may be a shape asshown in FIG. 12. A warm stop 110 being a modification example of thepresent invention shown in the same drawing has a reflective face 115having an arc cross section along the optical axis of the relay lens 9and being rotationally symmetric with respect to the optical axis of therelay lens 9, which is formed from an opening edge of an opening 114 tothe outside and on the imaging element 16 side. This reflective face 115has such a shape that the center of the arc formed by the reflectiveface 115 is located at the edge on the detection plane of the imagingelement 16 and that normals to the reflective face 115 extend to theedge of the imaging element 16 located in the same direction amongdirections perpendicular to the optical axis, without intersecting withthe optical axis. However, this reflective face 115 is not alwayslimited to the shape in which the center of the arc is located at theedge of the imaging element 16, but it may be a shape in which it islocated nearer the central region from the edge of the imaging element16. The warm stop 110 having this reflective face 115 also implementssuch setting as to project an image of the cold stop 13 onto the imagingelement 16 and not to project an image of the imaging element 16 itselfthereto. Specifically, it can prevent a part of a signal or noiseincident through the opening 114 of the warm stop 110 from beingspecularly reflected on the surface of the imaging element 16, furtherbeing reflected on the warm stop 110, and thereafter returning to theimaging element 16. In addition, when the normals at respective pointson the reflective face 115 are directed to the inside as much aspossible, it can project an image of the cold part, i.e., the cold stop13 onto the imaging element 16.

The shape of the reflective face of the warm stop may also be a shape asshown in FIG. 13. A warm stop 210 being a modification example of thepresent invention shown in the same drawing has a reflective face 215having an arc cross section along the optical axis of the relay lens 9and being rotationally symmetric with respect to the optical axis of therelay lens 9, which is formed from an opening edge of an opening 214 tothe outside and on the imaging element 16 side. This reflective face 215has such a shape that the center of the arc formed by the reflectiveface 215 is located at the edge on the opposite side on the detectionplane of the imaging element 16 and that normals to the reflective face215 extend to the edge of the imaging element 16 located in the oppositedirection among directions perpendicular to the optical axis, whileintersecting with the optical axis. However, this reflective face 215 isnot always limited to the shape in which the center of the arc islocated at the edge of the imaging element 16, but it may be a shape inwhich it is located nearer the central region from the edge of theimaging element 16. The warm stop 210 having this reflective face 215also implements such setting as to project an image of the cold stop 13onto the imaging element 16 and not to project an image of the imagingelement 16 itself thereto as the warm stop 110 does.

The shape of the reflective face of the warm stop may also be a shapesuch as a combination of the shapes of the reflective face 115 and thereflective face 215, as shown in FIG. 14. The warm stop 310 being amodification example of the present invention shown in the same drawinghas two reflective faces 315 a, 315 b formed from an opening edge of anopening 314 to the outside and in the named order on the imaging element16 side. This reflective face 315 a has the same cross-sectional shapeas the reflective face 115 and such a shape that the center of the arcformed by the reflective face 315 a is located at the edge on thedetection plane of the imaging element 16. The reflective face 315 b hasthe same cross-sectional shape as the reflective face 215 and such ashape that the center of the arc formed by the reflective face 315 b islocated at the edge on the opposite side on the detection plane of theimaging element 16. The warm stop 310 having this reflective face 315also implements such setting as to project an image of the cold stop 13onto the imaging element 16 and not to project an image of the imagingelement 16 itself thereto as the warm stops 110, 210 do.

The shape of the reflective face of the warm stop may also be a shape asshown in FIG. 15. The warm stop 90 being a modification example of thepresent invention shown in the same figure has an opening 94 formed withan inner wall diverging toward the imaging element 16, and a reflectiveface 95 is formed on the inner wall of this opening 94. This reflectiveface 95 has a conical surface shape whose inclination relative to a faceincluding an opening edge of the opening 94 is constant, and thisinclination and the thickness of the warm stop 90 (the length of theopening 94) are set so as to project an image of the cold stop 13 ontothe imaging element 16 and not to project an image of the imagingelement 16 itself thereto.

The microscope device 1 may be equipped with a driving mechanism fordriving the support member 11 of the optical device for microscopicobservation 4, 22, 44, or 64, and a control circuit for controlling thedriving mechanism, and the control circuit may control the drivingmechanism so as to automatically insert or remove the warm stop 10,based on data of objective lenses registered in advance.

The microscope device 1 can be applied to targets of various objectsthat emit light of specific wavelength such as infrared light, e.g.,semiconductors, inorganic and organic substances to emit fluorescence orphosphorescence, etc., as the sample S of observation target.

A preferred configuration herein is such that the second magnificationis higher than the first magnification. In this case, the observationmagnification of the object can be changed over between the lowmagnification and the high magnification.

Another preferred configuration is such that the support member isconfigured so that the second opening of the warm stop can be insertedor removed at the position proximate to the object-side window of thevacuum vessel. When the device is equipped with such a support member,the diameter can be narrowed down in accordance with the image-sidenumerical aperture in use of the optical system with the secondmagnification.

Furthermore, another preferred configuration is such that the supportmember is configured so that the second opening of the warm stop can beinserted or removed at the position corresponding to the pupil positionof the optical system with the second magnification. When the device isequipped with such a support member, the diameter can be narrowed downin accordance with the image-side numerical aperture in use of theoptical system with the second magnification.

Moreover, another preferred configuration is such that the reflectivesurface of the warm stop is formed so as to project an image of the coldstop onto the imaging element and so as not to project an image of theimaging element itself thereto. By this configuration, the reflectivesurface provided in the warm stop causes the imaging element to observethe light from the cold stop but not to observe the light reflected fromthe imaging element. This can reduce both of spot noise and backgroundnoise in the detected image by the imaging element when the object-sideoptical system is used as changed over from one to another.

Furthermore, another preferred configuration is such that the reflectivesurface of the warm stop comprises the first face with the gentle sloperelative to the face including the opening and the second face with thesteep slope relative to the same face continuously formed from theopening side to the outside. When this configuration is adopted, thesecond face allows such setting that the imaging element does notobserve light from the part other than the cold stop and the first facemakes the reflected light by the imaging element itself unlikely to beobserved.

Still another preferred configuration is such that the reflectivesurface is formed in a concave shape at least in part. In this case, itis feasible to readily set the shape to reflect the light from the coldstop to the imaging element.

Furthermore, another preferred configuration is such that the devicefurther comprises the auxiliary warm stop provided outside the vacuumvessel between the warm stop and the cold stop and being the stop memberhaving the opening facing the opening of the warm stop and having thereflective surface formed on the imaging element side. Thisconfiguration can prevent the reflected light from the imaging elementfrom impinging again on the imaging element and can make the light fromthe high-temperature part less likely to impinge on the imaging elementeven with decrease in the diameter of the warm stop.

Moreover, still another preferred configuration is such that the radiusof curvature of the reflective surface of the warm stop is not more thantwice the distance between the imaging element and the warm stop. Whenthis configuration is adopted, the light from the high-temperature partoutside the cold stop can be made less likely to impinge on the imagingelement.

Furthermore, another preferred configuration is such that the reflectivesurface of the warm stop or the auxiliary warm stop is formed in aplanar shape at least in part. In this case, the simple shape canprevent the light reflected by the imaging element itself, fromimpinging on the imaging element.

Another preferred configuration is such that the reflective surface ofthe warm stop or the auxiliary warm stop is formed in a conical surfaceshape at least in part. In this case as well, the simple shape canprevent the light reflected by the imaging element itself, fromimpinging on the imaging element.

INDUSTRIAL APPLICABILITY

The present invention has use application to the optical devices formicroscopic observation provided for enlarged observation of light froman object and enables reduction of background noise with use of opticalsystems of multiple observation magnifications and easy implementationof downsizing of the device.

REFERENCE SIGNS LIST

3 camera (imaging element); 4, 22, 44, 64 optical device for microscopicobservation; 5 microscope optical system; 7 macro optical system; 8micro optical system; 10, 90, 110, 210, 310 warm stop; 11 supportmember; 13 cold stop; 13 d, 13 e opening; 14, 114, 214, 314 opening; 15,15 a, 15 b, 15 c, 15 d, 115, 215, 315 a, 315 b reflective surface orface; 16 imaging element; 70 auxiliary warm stop; 74 opening; 75reflective surface.

1. A microscope system for imaging an image of an object, comprising: amicroscope optical system comprising a first optical system having afirst magnification and a second optical system having a secondmagnification which is higher than the first magnification, andconfigured to enable a changeover so as to locate either of the firstoptical system and the second optical system to face to the object; adetector arranged in a vacuum vessel and configured to detect light fromthe object; and an aperture corresponding to the second optical system,wherein a shape at the aperture becomes thinner toward a tip, whereinthe aperture is removed from the optical path when the first opticalsystem is located so as to face to the object and the aperture isinserted onto the optical path when the second optical system is locatedso as to face the object. 2-13. (canceled)
 14. The microscope systemaccording to claim 1, further comprising a support member including theaperture.
 15. The microscope system according to claim 14, wherein thesupport member includes a plurality of apertures.
 16. The microscopesystem according to claim 1, further comprising a driving mechanism fordriving the aperture and a control circuit for controlling the drivingmechanism.
 17. The microscope system according to claim 1, wherein theaperture is configured to be inserted or removed at a positioncorresponding to a pupil position of the second optical system.
 18. Themicroscope system according to claim 1, wherein the detector is a cameraconfigured to detect infrared light emitted from a sample.
 19. Themicroscope system according to claim 1, wherein the object is asemiconductor device
 20. A microscopic observation method for imaging animage of an object using a microscope system comprising a microscopeoptical system comprising a first optical system having a firstmagnification and a second optical system having a second magnificationwhich is higher than the first magnification, an aperture correspondingto the second optical system, wherein a shape at the aperture becomesthinner toward a tip, and a detector arranged in the vacuum vessel, themethod comprising: locating the first optical system so as to face tothe object and removing the aperture from an optical path of the lightfrom the object; by the detector, imaging the light passing through thefirst optical system; locating the second optical system so as to faceto the object and inserting the aperture onto the optical path; and bythe detector, imaging the light passing through the second opticalsystem and the aperture.
 21. The microscopic observation methodaccording to claim 20, wherein the aperture is inserted or removed at aposition corresponding to a pupil position of the second optical system.22. The microscopic observation method according to claim 20, whereinthe detector is a camera configured to detect infrared light emittedfrom a sample.
 23. The microscopic observation method according to claim20, wherein the object is a semiconductor device.
 24. A microscopesystem for imaging an image of an object, comprising: a microscopeoptical system comprising a first optical system having a firstmagnification and a second optical system having a second magnificationwhich is higher than the first magnification, and configured to enable achangeover so as to locate either of the first optical system and thesecond optical system to face to the object; a detector arranged in avacuum vessel and configured to detect light from the object; and anaperture having a first opening and a second opening which is smallerthan the first opening, and corresponding to the second optical system,wherein the aperture is removed from the optical path when the firstoptical system is located so as to face to the object and the apertureis inserted onto the optical path when the second optical system islocated so as to face to the object.